Apr 22, 2014 11:08 AM EDT By Jaleesa Baulkman, UniversityHerald Reporter

Older parents may be more likely to have a child who develops an autism spectrum disorder than younger parents, according to a recent study.

Researchers from the Drexel University School of Public Health in Philadelphia and Karolinska Institute in Sweden found that autism risk grows steadily with fathers' increasing age, but accelerates with mothers' age after 30.

Brian Lee, senior author of the study, said that multiple mechanisms could be in play to account for the different patterns of risk, including environmental risk factors occurring in women after age 30. Factors such as complications in pregnancy could also underlie the effect of mothers' ages on a child's autism risk but not a paternal age effect.

For the study, researchers analyzed a large population registry sample of more than 417,000 children born in Sweden between 1984 and 2003. They also used a particularly comprehensive case-finding approach, "to identify more ASD cases than other studies might, based on all pathways to care in a socialized health system," according to a press release.

The researchers' goal was to study these parental age effects in more detail by looking at possible differing risks of the development of [autism spectrum disorder] with and without intellectual disability - one of the most serious comorbid diagnoses with [autism spectrum disorder] , with a significant impact on functional status in life.

"When considering risk factors, we can't necessarily lump all ASD cases together, even though they fall under a broad umbrella of autism," Lee said. "We need to keep an open mind in case intellectual disability might be a marker of a different underlying mechanism."

Lee said that although age effects are important indicators of risk at the population level that could eventually help researchers identify preventable causes of disability, they aren't very significant for a couple's family planning because the overall risk remains low.

"The absolute risk of having a child with ASD is still approximately 1 in 100 in the overall sample, and less than 2 in 100 even for mothers up to age 45," according to Lee.

The findings were recently published in the International Journal of Epidemiology. 

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